1. Field of the Invention
The present invention relates to a method of manufacturing granulated silica powder, and a method of manufacturing a vitreous silica crucible.
2. Description of the Related Art
In one example, a method of manufacturing a vitreous silica crucible includes a silica powder layer forming process for forming a silica powder layer by depositing silica powder having an average particle diameter of approximately 300 μm on the inner surface of a rotating mold, and an arc fusing process for arc fusing the silica powder layer while depressurizing the silica powder layer from the mold side (hereinafter, this method is referred to as “rotating mold pressure reduction method”). Furthermore, in order to make uniform the height of the crucible after the arc fusing process, a cutting-off process for cutting off the upper end portion of the crucible is carried out.
In manufacturing a two-layer structure crucible having a transparent vitreous silica layer substantially not containing bubbles (hereinafter, referred to as “transparent layer”) on the inner side of the crucible, and a vitreous silica layer containing bubbles (hereinafter, referred to as “bubble-containing layer”) on the outer side of the crucible, a transparent layer is formed by removing bubbles by depressurizing the silica powder layer at the beginning of the arc fusing process, and thereafter, a bubble-containing layer containing residual bubbles is formed by weakening depressurization.
In manufacturing a crucible, the rim cutting process for cutting off the upper end of a crucible is carried out on all crucibles, and a large amount of waste vitreous silica is generated in the process. Furthermore, the crucible obtained in the arc fusing process is sometimes not in compliance with the specifications, and in a case where the crucible cannot be modified to meet the specifications, the crucible is usually scrapped to generate waste vitreous silica.
Related references to the present invention are JP-A-2001-220157, and JP-A-h7-33548.